Tectonic triggers for the intrusion of the Great Dyke (Zimbabwe) and Bushveld Complex (South Africa)

Abstract Two of the world’s largest layered igneous complexes – the Great Dyke in Zimbabwe (2 575 ± 0.7 Ma) and the Bushveld Complex in South Africa (2 056 ± 1 Ma) were intruded broadly coeval with major compressive events associated with orogenic belts along the margins of their host cratons (the Zimbabwe and Kaapvaal cratons, respectively). Thus, the Northern Marginal Zone of the Limpopo Belt, which bounds the Zimbabwe Craton in the south, experienced a major north-northwest shortening event at some time between 2.74 and 2.57 Ga, with a metamorphic peak at ~2.59 Ga. Therefore, this time span includes the emplacement of the Great Dyke, and such shortening provides a mechanism for the initiation of the north-northeast-oriented fault system exploited by this major layered intrusion and parallel satellite dykes. Emplacement of the Bushveld Complex was broadly coeval with a major transpressive orogeny, linked to continental scale transcurrent movement along the Palala Shear Zone in the Limpopo Belt, immediately north of the Kaapvaal Craton, between 2.05 and 1.95 Ga. The Magondi Belt was thrust eastwards over the Zimbabwe Craton between 2.06 and 1.96 Ga. Granite in the Okwa inlier, located on the western margin of the Kaapvaal Craton and dated at 2.05 Ga, and acid volcanics near Kokong village, western Botswana, dated at 2.06 to 2.05 Ga, suggest that deformation and igneous activity linked to the Magondi Orogeny extended to the south, along the western margin of the Kaapvaal Craton. This is consistent with a tectonic reconstruction of the Palaeoproterozoic Superia supercontinent. Orogenic events on the craton margin reactivated major intracratonic, continent-scale fault systems, like the Thabazimbi-Murchison Lineament (TML), inferred to have been a feeder for Bushveld magmas. The synchronicity between the emplacement ages of the Great Dyke and the Bushveld Complex and horizontal stresses associated with their respective craton margins suggests that tectonic processes played an important role in initiating the magmatic activity which resulted in the emplacement of two of the largest layered igneous complexes on Earth. This in turn raises the question of the link between plate-margin tectonic events and mantle plumes.